Last modified: 7 May 2020

URL: https://cxc.cfa.harvard.edu/ciao/caveats/ephem.html

Caveat: Ephemeris Accuracy



The CXC's goal is to distribute data products within a week of the observation. Since the definitive orbit ephemeris data (orbit*eph1.fits) are usually not available until a week after the observation ends, a predictive orbit ephemeris (orbit*eph0.fits) is shipped with all newly acquired data. The definitive ephemeris data are provided for archival datasets.

Use of predictive ephemerides is sufficient for most purposes, since the accuracy for the first week is certainly better than 300 km, or 1 ms. The exception is applying barycenter corrections to fast pulsars.

Users with new data sets can retrieve the definitive ephemeris files through the Chandra Data Archive Search and Retrieval (ChaSeR) interface approximately a week after the observation was performed.